Abstract:
The present project investigated and proved the concept of developing a novel
BioMEMS glucose micro-biosensor using a simple one-step microfabrication process of
the widely used SU-8 polymer. More specifically, the study focused on the investigation
of the suitability of the SU-8 polymer as a matrix for enzyme immobilisation that is
carried out during the microfabrication process. A comparative study between
commercially available SU-8 and “customised” SU-8 solutions showed that the
optimum concentration of photo-initiator for stress reduction can be achieved easier
with “customised” SU-8 solutions. The most appropriate type of microstructure for the
SU-8 matrix and the corresponding required microfabrication process were defined and
encapsulation of the enzyme GOx in the SU-8 solution was accomplished. A detailed
experimental investigation of the immobilised enzyme’s activity inside the SU-8 matrix,
was carried out using amperometric detection of hydrogen peroxide in a 3-electrode setup.
SU-8 films were immersed in a buffer solution and the platinum working electrode
was brought in close contact with the film. Films without enzyme showed negligible
variation in current upon the addition of glucose, as opposed to films with encapsulated
enzyme which showed a very clear increase in current. Experiments using films of
increased thickness or enzyme concentration, showed a higher response, thus proving
that the enzyme remained active not only on the film’s surface, but inside the matrix as
well. In the fluorescence spectroscopy experiments, the utilisation of the tris (4,7-
diphenyl-1,10-phenanthroline) ruthenium(II) dichloride oxygen indicator, which was
also captured in the polymer matrix during the microfabrication process, was proven to
be very sensitive to glucose concentration changes during the glucose oxidation and
there was no photo-bleaching.
The experimental investigations proved that the proposed concept of using SU-8
matrices for the immobilisation of biomolecules, is a valid proposal for the construction
of a BioMEMS glucose biosensor. An important outcome was the successful
immobilisation of glucose oxidase in SU-8 microfabricated structures. The enzyme still
showed activity despite the “hostile” conditions during microfabrication The proof of
principle of enzyme immobilisation in SU-8 films opens up new possibilities for
combining BioMEMS with biosensors and organic electronics.
